Several phenotypes of severe diseases of the myocardium (or of skeletal muscles) are associated with an impairment of the sarcomere structure in the cardiomyocytes (or myocytes, respectively). For the sake of simplicity, in the following only cardiomyocytes are referred to. In cardiomyocytes, the sarcomere is the smallest subunit which is able to contract and relax.
A sarcomere is schematically shown in FIG. 1 (relaxed state) and FIG. 2 (contracted state). Sarcomere 1 is bounded by two z-disks 10 and further comprises two inter-digitized filament systems. The thin filaments of the first filament system of the two inter-digitized filament systems are composed of hexameric actin strands 11, the thick filaments of the second filament system of the two inter-digitized filament systems are composed of hexameric myosin strands 12. The myosin strands 12 are attached to the two z-disks 10 through two elastic elements 13 composed of protein titin. Upon hydrolysis of ATP (Adenosinetriphosphate), the motor protein myosin of the myosin strands 12 undergoes a conformational change which is converted to a power stroke that shifts the actin strands 11, leading to contraction of the sarcomere 1 (see FIG. 2). Contraction occurring for a large plurality of such sarcomeres 1 leads to contraction of the myocardium, while the reverse process leads to relaxation of the myocardium.
This contractile motion can already be observed in mature cultured living cardiomyocytes which exhibit spontaneous and synchronized beating, and this spontaneous and synchronized beating of the living cardiomyocytes can be used to characterize the mature development state of the living cardiomyocytes.
In fixed cardiomyocytes the structural integrity of the sarcomere structures is indicative of the mature development state of the cardiomyocytes. Fixing the cardiomyocytes may be performed, for example, by adding detergent to the living cardiomyocytes whereby the cell membranes of the living cardiomyocytes get damaged (the living cardiomyocytes are killed) and by adding formaldehyde whereby the proteins contained in the cardiomyocytes are cross-linked, however, the structures of the proteins in the cardiomyocytes are maintained and remain fixed.
For identifying potential drug candidate substances against diseases of the myocardium which are associated with impairment of the sarcomere structures, in vitro experiments are conducted in which the living cardiomyocytes are stressed by adding substances like glucose and/or endothelin until the cardiomyocytes lose their ability to beat without killing the cardiomyocytes (simulation of a cardiomyopathy). Thereafter, a drug candidate substance is added to the stressed cardiomyocytes in order to examine whether or not the drug candidate substance has a recovering effect on the cardiomyocytes, this recovering effect resulting in the cardiomyocytes starting to beat again. For this examination, a small movie of the cardiomyocytes is recorded and is analyzed as to whether the cardiomyocytes have started to beat again (the beating contraction and subsequent relaxation cycles can only be assessed when analyzing a movie). As outlined, however, this analysis of the movies must be performed by a person watching the movies, this being time- and resource-consuming. In addition, the humans watching and analyzing the movies must have the required education and skill.
Alternatively, after the drug candidate substance has been added to the living cardiomyocytes, and after these have been fixed subsequently, the fixed cardiomyocytes are examined for the presence of periodic structures of sarcomeres. Such periodic structures of sarcomeres are indicative of the cardiomyocytes having recovered prior to fixation. This can be performed by taking an image of the fixed cardiomyocytes that must be carefully analyzed by humans through optical inspection. This is again very time- and resource-consuming, and the person performing the optical inspection must have the required education and skill. Even then the images are very difficult to analyze.